Send an event to the page load metrics to track resource starting.

chrome/browser/page_load_metrics/page_load_metrics_observer.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_PAGE_LOAD_METRICS_PAGE_LOAD_METRICS_OBSERVER_H_
 #define CHROME_BROWSER_PAGE_LOAD_METRICS_PAGE_LOAD_METRICS_OBSERVER_H_
 
 #include <string>
 
 #include "base/macros.h"
@@ skipping 178 matching lines @@
 
   // Extra information supplied to the page load metrics system from the
   // renderer for the main frame.
   const PageLoadMetadata main_frame_metadata;
 
   // PageLoadMetadata for child frames of the current page load.
   const PageLoadMetadata child_frame_metadata;
 };
 
 // Container for various information about a request within a page load.
-struct ExtraRequestInfo {
-  ExtraRequestInfo(bool was_cached,
-                   int64_t raw_body_bytes,
-                   bool data_reduction_proxy_used,
-                   int64_t original_network_content_length);
+struct ExtraRequestCompleteInfo {
+  ExtraRequestCompleteInfo(bool was_cached,
+                           int64_t raw_body_bytes,
+                           bool data_reduction_proxy_used,
+                           int64_t original_network_content_length,
+                           content::ResourceType found_type);
 
-  ExtraRequestInfo(const ExtraRequestInfo& other);
+  ExtraRequestCompleteInfo(const ExtraRequestCompleteInfo& other);
 
-  ~ExtraRequestInfo();
+  ~ExtraRequestCompleteInfo();
 
   // True if the resource was loaded from cache.
   const bool was_cached;
 
   // The number of body (not header) prefilter bytes.
   const int64_t raw_body_bytes;
 
   // Whether this request used Data Reduction Proxy.
   const bool data_reduction_proxy_used;
 
   // The number of body (not header) bytes that the data reduction proxy saw
   // before it compressed the requests.
   const int64_t original_network_content_length;
+
+  // The type of the request as gleaned from the
+  // ChromeResourceDispatcherHostDelegate.

[RyanSturm, 2017/04/14 20:08:43]

I'd adjust this comment to say "from ResourceRequestInfo" if you want to specify
the source of the value. Same below.

[Pete Williamson, 2017/04/17 18:53:11]

Done in both places.

+  const content::ResourceType resource_type;
+};
+
+// Container for various information about a request within a page load.
+struct ExtraRequestStartInfo {
+  explicit ExtraRequestStartInfo(content::ResourceType type);
+
+  ExtraRequestStartInfo(const ExtraRequestStartInfo& other);
+
+  ~ExtraRequestStartInfo();
+
+  // The type of the request as gleaned from the
+  // ChromeResourceDispatcherHostDelegate.
+  const content::ResourceType resource_type;
 };
 
 // Interface for PageLoadMetrics observers. All instances of this class are
 // owned by the PageLoadTracker tracking a page load.
 class PageLoadMetricsObserver {
  public:
   // ObservePolicy is used as a return value on some PageLoadMetricsObserver
   // callbacks to indicate whether the observer would like to continue observing
   // metric callbacks. Observers that wish to continue observing metric
   // callbacks should return CONTINUE_OBSERVING; observers that wish to stop
@@ skipping 137 matching lines @@
   // frequently on Android).
   virtual void OnComplete(const PageLoadTiming& timing,
                           const PageLoadExtraInfo& extra_info) {}
 
   // OnFailedProvisionalLoad is invoked for tracked page loads that did not
   // commit, immediately before the observer is deleted.
   virtual void OnFailedProvisionalLoad(
       const FailedProvisionalLoadInfo& failed_provisional_load_info,
       const PageLoadExtraInfo& extra_info) {}
 
+  // Called whenever a request load begins.
+  virtual void OnStartedResource(
+      const ExtraRequestStartInfo& extra_request_start_info) {}
+
   // Called whenever a request is loaded for this page load.
-  virtual void OnLoadedResource(const ExtraRequestInfo& extra_request_info) {}
+  virtual void OnLoadedResource(
+      const ExtraRequestCompleteInfo& extra_request_complete_info) {}
 };
 
 }  // namespace page_load_metrics
 
 #endif  // CHROME_BROWSER_PAGE_LOAD_METRICS_PAGE_LOAD_METRICS_OBSERVER_H_